Prefer `flat_map` over `map` + `flatten`

Convert several occurrences of `map` + `flatten` to
`flat_map` where applicable.

app/models/concerns/protected_ref.rb

@@ -47,7 +47,7 @@ module ProtectedRef
     def access_levels_for_ref(ref, action:, protected_refs: nil)
       self.matching(ref, protected_refs: protected_refs)
-        .map(&:"#{action}_access_levels").flatten
+        .flat_map(&:"#{action}_access_levels")
     end
     # Returns all protected refs that match the given ref name.

app/models/group.rb

@@ -388,7 +388,7 @@ class Group < Namespace
     variables = Ci::GroupVariable.where(group: list_of_ids)
     variables = variables.unprotected unless project.protected_for?(ref)
     variables = variables.group_by(&:group_id)
-    list_of_ids.reverse.map { |group| variables[group.id] }.compact.flatten
+    list_of_ids.reverse.flat_map { |group| variables[group.id] }.compact
   end
   def group_member(user)

app/serializers/stage_entity.rb

@@ -59,14 +59,14 @@ class StageEntity < Grape::Entity
   end
   def latest_statuses
-    HasStatus::ORDERED_STATUSES.map do |ordered_status|
+    HasStatus::ORDERED_STATUSES.flat_map do |ordered_status|
       grouped_statuses.fetch(ordered_status, [])
-    end.flatten
+    end
   end
   def retried_statuses
-    HasStatus::ORDERED_STATUSES.map do |ordered_status|
+    HasStatus::ORDERED_STATUSES.flat_map do |ordered_status|
       grouped_retried_statuses.fetch(ordered_status, [])
-    end.flatten
+    end
   end
 end

app/services/ci/process_pipeline_service.rb

@@ -10,13 +10,13 @@ module Ci
       update_retried
       new_builds =
-        stage_indexes_of_created_processables.map do |index|
+        stage_indexes_of_created_processables.flat_map do |index|
           process_stage(index)
         end
       @pipeline.update_status
-      new_builds.flatten.any?
+      new_builds.any?
     end
     private

lib/api/validations/types/labels_list.rb

@@ -10,7 +10,7 @@ module API
             when String
               value.split(',').map(&:strip)
             when Array
-              value.map { |v| v.to_s.split(',').map(&:strip) }.flatten
+              value.flat_map { |v| v.to_s.split(',').map(&:strip) }
             when LabelsList
               value
             else

lib/banzai/reference_redactor.rb

@@ -33,7 +33,7 @@ module Banzai
     #
     # data - An Array of a Hashes mapping an HTML document to nodes to redact.
     def redact_document_nodes(all_document_nodes)
-      all_nodes = all_document_nodes.map { |x| x[:nodes] }.flatten
+      all_nodes = all_document_nodes.flat_map { |x| x[:nodes] }
       visible = nodes_visible_to_user(all_nodes)
       metadata = []

lib/gitlab/background_migration/backfill_project_repositories.rb

@@ -40,7 +40,7 @@ module Gitlab
         end
         def reload!
-          @shards = Hash[*Shard.all.map { |shard| [shard.name, shard.id] }.flatten]
+          @shards = Hash[*Shard.all.flat_map { |shard| [shard.name, shard.id] }]
         end
       end

lib/gitlab/ci/config/normalizer.rb

@@ -46,7 +46,7 @@ module Gitlab
           parallelized_job_names = @parallelized_jobs.keys.map(&:to_s)
           parallelized_config.each_with_object({}) do |(job_name, config), hash|
             if config[:dependencies] && (intersection = config[:dependencies] & parallelized_job_names).any?
-              parallelized_deps = intersection.map { |dep| @parallelized_jobs[dep.to_sym].map(&:first) }.flatten
+              parallelized_deps = intersection.flat_map { |dep| @parallelized_jobs[dep.to_sym].map(&:first) }
               deps = config[:dependencies] - intersection + parallelized_deps
               hash[job_name] = config.merge(dependencies: deps)
             else

lib/gitlab/ci/status/factory.rb

@@ -34,11 +34,9 @@ module Gitlab
         def extended_statuses
           return @extended_statuses if defined?(@extended_statuses)
-          groups = self.class.extended_statuses.map do |group|
+          @extended_statuses = self.class.extended_statuses.flat_map do |group|
             Array(group).find { |status| status.matches?(@subject, @user) }
-          end
-
-          @extended_statuses = groups.flatten.compact
+          end.compact
         end
         def self.extended_statuses